1. Field of the Invention
The invention relates to an improved composite histologic tissue receptacle and embedding structure which serves as an integral, perforate, shallow depth, receptacle for holding tissue during the processing thereof, as a mold for embedding processed tissue in a paraffin body preparatory to mounting in the microtome, as a means for aligning and holding the embedded specimen in the microtome and as a receptacle for protecting and storing the embedded tissue after portions of the same have been severed by the microtome.
2. Description of the Prior Art
A composite tissue receptacle and embedding structure of the type most closely related to this invention is taught by U.S. Pat. No. 3,456,300. The structure taught by this patent includes an open mold, a base pan which is detachably secured onto either open end of the open mold and a perforated top which is detachably secured onto the other end of the open mold all of which forms an integral closure for the specimen. The open mold element of the patent is rectangular in cross section and includes four smooth surfaced perpendicular and interconnecting walls. An outer surface of the upper mold is etched in order to receive indicia by means of an ordinary pencil. The base pan of the patent is shaped substantially like a rectangular open topped box with a thin, heat conducting, flat bottom surface and an indented ledge which extends downwardly from the inside edge of the base pan walls so as to "snap fit" onto either end of the open mold. The flat bottom surface is provided with openings which allow the processing fluids to pass through the composite tissue embedding structure. The perforated top of the patent is detachably secured to the other end of the open mold and consists of a perforated rectangular shaped surface having outwardly projecting sides which "snap fit" over the end of the open mold. The top element in conjunction with the mold and pan elements of the patent forms an integral perforate structure which can be inverted, tilted and otherwise handled without coming apart.
Since the device of the present invention specifically improves on the device of the U.S. Pat. No. 3,456,300, the operation of the device of the patent will next be explained to more fully appreciate the prior art. In operation, a tissue specimen to be pathologically examined is placed in the base pan of the prior patent device without regard to any particular position. One end of the open mold is "snap fastened" to the base pan and the other end of the mold is "snap fastened" to the perforated top to provide the mentioned integral, perforate enclosure for the specimen. The serial number of the tissue specimen is marked by means of a graphite pencil onto an etched surface of the open mold. The mold with the top cover and base pan "snap fastened" to it at either end at this stage provides a perforate tissue processing receptacle. The composite tissue embedding structure is placed sequentially into various treating liquids and finally into a paraffin bath where paraffin is transferred by osmosis into the tissue cells.
As the description proceeds, many similarities will be observed between the construction and use of the device of the U.S. Pat. No. 3,456,300 and the present invention. However, what is important to observe is that the patent device makes no provision for telescoping the pan section into the mold section for reducing the amount of space occupied during processing when the three elements form a processing receptacle. With an increasing use of the patent device the need to process greater and greater numbers of receptacles in the processing chambers has become increasingly critical and important. The relative depth of the three elements when assembled as a processing receptacle thus becomes of increasing importance since this depth to a major extent determines how many receptacles can be processed simultantously. The bottom outside surface is next wiped to remove excess paraffin. At this stage, a thin film of paraffin coats the bottom inside surface of the boat receptacle and while the paraffin is hot and tacky, the perforated top is removed and may be discarded as a disposable item. After adding additional liquid paraffin, the specimen is repositioned on the flat bottom surface of the base pan into a precise cutting position. The paraffin is allowed to harden so that the precise plane of the specimen along which it is to be severed is presented to the microtome blade. The positioning of the specimen is most important for frequently the only means for determining the malignancy of tissue is by properly selecting the plane of severance. As an alternative, the thin coating of paraffin clinging to the bottom surface of the boat receptacle may be allowed to harden and later reheated and the tissue specimen repositioned. In either case, the tissue specimen is positioned while the mold and base pan are "snap fastened" together.
After the tissue specimen is selectively positioned in the base pan, melted paraffin is poured into the base pan through the open end of the open mold to a level substantially adjacent that open end thus completely embedding the tissue specimen. After the paraffin hardens and approaches room temperature, the tissue specimen is presented to the blade of the microtome. Thus, while the base pan remains "snap fastened" to the mold, the composite structure is placed in the jaws of the microtome with the jaws abuted against the exposed surface of the edges of the base pan which act to align the cutting surface of the paraffin block with the microtome blade. After such alignment, the jaws of the microtome are tightened onto the open mold and the base pan is removed which exposes the bottom surface of the block for cutting. After one or several sections are sliced from the tissue specimen by the microtome knife, the base pan is "snap fastened" back onto the open mold so as to cover the exposed tissue specimen surface and prevent the same from becoming soiled or damaged during the usual extended storage for possible later reference to the same patient. At any later time, the tissue specimen may be removed from storage and made available for further sectioning and in the interim the base pan acts as a protective cover.
Further prior art includes devices for processing tissue in plastic or metal perforated containers and for embedding the tissue with paraffin in separate plastic, paper, or metal pans. The device of U.S. Pat. No. 3,674,396, for example, uses a perforated plastic container with a removable metal perforated cover for processing. This metal cover is removed after processing and the tissue specimen is transferred to a metal pan for embedding. The container is then placed in the metal pan and the unit is filled with paraffin for embedding. These devices offer some advantage in providing a relatively shallow depth receptacle for processing but lack the advantage of being able to use the same device for all the steps of processing, embedding, slicing and storing. The devices referred to in U.S. Pat. No. 3,456,300 and in a prior U.S. Pat. No. 2,996,762 mark an advancement over this latter type art since it is desirable to provide an identification mold section which can be used through tissue processing with a perforated top and a pan section, as one unit, for holding and transporting the tissue specimen through the various processing liquids, then as a mold for paraffin embedding the specimen and as a holder for holding the embedded specimen in a microtome during slicing and as a cover for protecting the remaining paraffin tissue block during storage.
Thus, while it can be said that the prior art device described in U.S. Pat. No. 3,456,300 represented a substantial improvement over other prior art devices, there has remained a substantial need to retain the multi-purpose advantages of the patent device but to reduce the amount of space required to process embedded specimens. Stated differently, larger and larger quantities of tissue specimens are being embedded in hospitals, pathology laboratories, and the like, which means that while the device of U.S. Pat. No. 3,456,300 has vastly improved the processing, embedding, and slicing procedures there still remains an critical problem of processing embedded specimens in a minimum of space.